I believe you should have went to "Edit" > "Export" and export it as a png.
Yeah, as Tariri said, that is exactly what you should have done. Although GIMP does freak out a little, maybe try downloading another program like Paint.NET (which is also free) and exporting it there, then you might be able to download it again. You have the new version like me so I don't see why this is happening. There are many ways of opening images to GIMP, so it could eventually find a way to work.
You could go to your documents, right click and ''Edit with GIMP''
You could open GIMP and then find File >> Open Recent >> yourdrawing.xcf (for example)
If that doesn't work try restarting your computer or installing the entire GIMP program again. Also, please refrain from double posting, just click ''Modify'' above your post if you need to add in or say something else. Good luck.